First question of the panel. Stephen: database bottlenecks get the attention but ActionView partials are often the hidden killer — a single extra partial can add 40% latency. Caio: the deeper issue is forgetting that framework black boxes are doing real work — loading big collections in memory (use find_each), serializing large objects into background jobs, etc. Maciej: fetching too much data, too many queries, or joining data from two sources in Ruby (re-implementing database algorithms on the application layer with nested loops or hashes).